Slips are used in downhole tools such as packers to retain the position of the tool. Slips can be provided in a cage where a sleeve has openings through which the slips extend, separated by structural components of the cage to give it the integrity needed to withstand forces applied during the operation of the tool. These conventional caged slip systems offer protection to the slips while running in the hole. Apart from protecting the slips during run-in, the cage itself typically serves as a pickup device when retrieving slips. One of the design drawbacks of existing caged slip systems is a limitation on the extendable diametrical range of the slips. The longitudinal elements which define the openings through which the slips extend also serve as travel stops. Since these longitudinal components require a predetermined structural strength, they cannot be thinned to allow additional slip extension. This concept is illustrated in FIG. 1 which shows the prior art. In FIG. 1 a prospective view of a slip 10 is shown. The cross-section of the slip 10 is U shaped and the longitudinal strip 12 extends within the U and acts as an outward travel stop for the caged slip 10. The openings or windows 14 are defined between the longitudinal strips 12. Accordingly, in the prior art, the requisite thickness of the longitudinal strips 12 limited the amount of outward travel of the slips 10. Additionally, in the prior art designs, the cones which would force the slips outwardly were located inside the cage as represented graphically by arrow 16. One such product is the Model SC-2P retrievable packer made by Baker Oil Tools. The placement of the cones within the cage defined by longitudinal members 12 reduced the available bearing area of the cones on the slips and therefore limited the capacity of the slips to resist differential forces which are present in the wellbore. Thus, these two significant limitations of prior caged slip designs amounted to lower performance ratings of the overall tool, as well as the need to have more tools available for varying sizes of casing. The reason for this was that depending on the casing weight per foot, its inside dimension would vary. Thus, different tools might be needed in the prior art to extend sufficiently far if lighter wall casing was in use.
Thus, some of the objectives of the present invention are to allow greater extension of the slips while retaining or expanding the ability of the slip system to withstand differential loads. Additionally, another objective is to allow within a given tool body size sufficient rangeability and slip extension so as to avoid stocking a large inventory of tools to handle a variety of situations. Another objective is to uniquely position the cone within the openings of the cage so that the cones extend outwardly as far as the outer extremity of the cage. All this is accomplished while at the same time retaining the beneficial qualities of a caged slip during run-in. Another objective, which is accomplished by putting the cones in the windows of the cage, allows the cage thickness to be increased to improve its tensile strength without reduction of the amount of slip extension. Finally, another objective is to be able to retain the slips to a predetermined extension diametrically outwardly. Thus, the slips are limited in radial extension to prevent them from escaping the cage if they are extended in an unsupported condition. Yet another objective of the present invention is to facilitate release of the slips by mechanically driving the lower cone out from the lowermost slips, as opposed to trying to pull and disengage slips off of a stationary cone. The objective of the release system is to be able to unsupport the slips, regardless of whether the mandrel of the packer is in tension or compression so that the slip is not pulled away from a cone when the cone forces the wickers of the slip against a casing or tubular. Those and other features of the present invention will become more apparent to those skilled in the art from a review of the preferred embodiment described below.